High-level ab initio, quantum chemical calculations on a number of hypervalent compounds—SFn-1Cl (n=1-6), SCln (n=1-6), PFnCl (n=2-4)—are presented in this dissertation. The bonding in the ground and excited states of these species was analyzed using generalized valence bond theory. These (and other) studies have led to a model—the recoupled pair bond (RPB) model—that provided much insight into the electronic structure of these compounds. Recoupled pair bonds are the basis for the unusual stability of hypervalent compounds. However, recoupled pair bonds were found to be common, explaining, e.g., the presence of unexpected excited states and the isomers found in the above species, many of which have never before been reported in the literature. The results of these studies will be discussed herein.
A second topic discussed herein is the impact of recoupled pair bonding on the reactivity of divalent sulfur compounds with molecular fluorine. Previously, researchers had found that the (CH3)2S + F2 reaction proceeded readily with a large rate constant, which is unusual for a reaction between two closed-shell molecules. We were able to explain the interesting experimental results for the (CH3)2S + F2 reaction as well as the H2S + F2 system, which was found to be nonreactive, experimentally. We will show, among other things, that nearly every critical structure for both systems, such as intermediates and products, has recoupled pair bonds. We verified that (CH3)2S + F2 should react readily. Indeed, there is no barrier to one reaction channel, while the H2S + F2 reaction has high barriers.